1. Field of the Invention
The present invention relates generally to a cooling fan, and more particularly relates to a cooling fan having low noise and having more optimized airflow distribution.
2. Description of Related Art
The computer CPU speed has been greatly increased in recent years due to a rapid progress in semi-conductor technologies. The chip surface heat flux is thus higher and higher accordingly. It is becoming a critical challenge on how to remove the heat so that the system can run reliably. The compact space with high flow resistance in a notebook computer environment is even more critical in the heat removal. A cooling fan with higher air pressure is frequently chosen under such a consideration.
A cooling fan 10 in related art is shown in FIGS. 3-4. The cooling fan 10 includes a housing 12 and an impeller 14 disposed in the housing 12. The housing 12 includes a planar base 121, a sidewall 122 perpendicularly and upwardly extending from the base 121 and a cap 123 covering the sidewall 122. The impeller 14 includes a hub 141 and a plurality of blades 142 radially and outwardly extending from the hub 141. An air channel 16 is formed between tip portions of the blades 142 and an inner surface of the sidewall 122. In operation of the cooling fan 10, the blades 142 rotate in the housing 12 to impel intake airflow to flow towards a near section A of an air outlet 124. The airflow leaves the air outlet 124 at the near section A and flows towards a far section C of the air outlet 124 through a middle section B.
Referring to FIG. 4 and following table 1, when the flow field of the airflow at the air outlet 124 is simulated by using computational fluid dynamics (CFD) software, it was found that the flux of the airflow at the near section A of the air outlet 124 occupies 53.9% of the total flux 2.84 cfm (cubic feet per minute) at the air outlet 124, which is more than the flux of the middle section B of the air outlet 124, which occupies 23.9% of the total flux, and far more than the flux of the far section C of the air outlet 124, which occupies 22.2% of the total flux. That is, the airflow non-uniformly flows through the air outlet 124.
TABLE 1Flux at section AFlux at section BFlux at section CFlux total (cfm)(cfm)(cfm)(cfm)2.841.530.680.63100%53.9%23.9%22.2%
Since the airflow non-uniformly flows through the air outlet 124, heat convections between the airflow and fins at sections A, B and C of the air outlet 124 are different from each other. However, the fins at the middle section B and the far section C of the air outlet 124 have the same heat dissipation capabilities as the fins at the near section A of the air outlet 124. Thus, there is a room for improving the heat dissipation efficiencies of the fins at the middle section B and the far section C of the air outlet 124. Moreover, there will be loud noises generated by the airflow flowing though the near section A of the air outlet 124, which violates the quiet requirement for the cooling fan 10.
For the foregoing reasons, there is a need for a cooling fan which has low noise and has more optimized airflow distribution.